President Lincoln CB-Radio

ALIGNMENT PROCEDURE

RECEIVER PORTION

Test equipment required:


Power Supply: 13,8 V	Dummy Load 8 ohm	AF VTVM	Oscilloscope
HF SSG:	28.000 MHz	1 kHz	30% Mod.

Preparation alignment:


NB SW	Off
PA SW	Off
Beep SW	Off
VOLUME	Max.
RIT	Middle position
Mode	AM
Squelch	Min.
DX/LOC	DX
Frequency	28.000 MHz

Step	Condition	Adjustment	Procedure
1	AM SSG 40dB 1 kHz Mod.	L101 L104 L113 L115 L105	Alignment of sensitivity. Adjust coils for maximum reading on the AF VTVM.
2	AM SSG 66dB 1 kHz Mod.	VR102	Alignment of Squelch. Set Squelsch to maximum. Adjust VR102 so that the squelch just breaks.
3	AM SSG 46dB No Mod.	VR101	Alignment of S-meter. Adjust VR101 so that "9" LCD just lights on.
4	FM SSG 1 mV 1.5 kHz Dev.	L401	Adjust L401 for maximum reading on the AF VTVM.
5	AM SSG 1 mV Noise Gen.	L203	Adjust L203 for maximum reading on the AF VTVM. Noise Generator output: 50 Hz SQ wave 2 V P-P.

Improved receive gain

Quieting of AM reception and improving gain of incoming signals is a common request from radio operators. In the first stages of the HF input 2SC1674 transistor can be found. This transistor is responsible for the amplification of a small detected signals. A problems exist if the transistor itself is noisy as is such the case of the 2SC1674 when compared to other low noise packages. Along with the amplification of the incoming signals is transistor noise. Replacement of this transistor with a higher gain, lower noise transistor greatly improves the signal to noise ratio of your receiver.
We will use an 2SC2999 transistor that has higher gain lower noise characteristic. Replace the 2SC1674 (Q101) with an 2SC2999 (or similar low noise and high gain transistor) to achieve this improved signal to noise ratio.
Re-Adjust L101
The gain will improved with more than 6dB with the same signal to noise ratio.